Patent GB-400418-A (GB)
Title: Improvements in servo-motors
IPC: B60T13/06
Filed: 1932-10-29
Abstract: 400,418. Servo-brakes; transmitting-mechanism. PIGANEAU, G. P., 152, Boulevard Malesherbes, Paris. Oct. 29, 1932, No. 30403. Convention date, Dec. 14, 1931. [Class 103 (i).] In a servo-motor, particularly adapted for applying the brakes of motor vehicles and of the kind comprising revolving heavy pieces or weights 22, 22a designed to operate the brake or other actuating - member 25 by centrifugal action, the effective force upon the member 25 is automatically prevented from exceeding a predetermined maximum value irrespective of the speed of the auxiliary element driving the heavy pieces, such result being attained by the provision, in the mechanism operated by the heavy pieces, of a spring or like elastic member 28 that yields when the limiting value of the force is reached. In the construction shown the rotating elements comprise a pulley 9, Fig. 1, pressed by a spring 12 into contact with the end 4 of a casing 1 keyed to a tubular sleeve 2, all these elements rotating on two slidable shafts 8, 24, the former of which bears against an abutment 27 for the spring 28, while the latter shaft bears against the lever 25. The heavy pieces 22, 22a are carried on Y-shaped members 21, 21a which slide transversely in slots 15, 15a in the sleeve 2 and have bevelled surfaces adapted to force wedge elements 16, 17 and consequently the shafts 8, 24 outwardly as the casing and weights are rotated. A spring 18 returns the parts to the normal position shown. In operation, if the pulley 9 is driven below the limiting speed, a force dependent upon the speed of rotation is exerted upon the lever 25 and a corresponding force upon the spring 28, which does not yield. If the speed exceeds the limiting valve, the force f<2> exerted upon the spring 28 is sufficient to compress the latter, the shaft 8 is permitted to move, a shoulder 30 thereon disengages the clutch or pulley 9, and the speed of rotation of the casing 1 falls. The equal and opposite force f upon the lever 25 is thus limited in value by the resistance of the spring 28, the effort of which is adjustable by a screw cap 29. The method of assembling the servo-motor in a brake mechanism is shown in Fig. 4. The pulley 9 is driven from a second pulley 39, a surface 37 on which is normally out of, but may be brought into, engagement with a coacting surface 38 on a disc-like extension 36 of a sleeve 33 driven by pinions 30, 32 from the intermediate gear shaft 31. The pulley 39 is brought into operation against the effort of a light spring 42 by means of a lever 48 connected by linkage 51, 55<1> to the brake pedal 52. When the pedal 52 is depressed the rotary brake shaft 54 to which the lever 25 is keyed is actuated through the medium of the rod 51 and lever 53 ; simultaneously the pulley 39 and servo-motor are brought into operation, and the braking effort transmitted by the shaft 54 thereby increased. An elastic connection 55 in the rod 55<1> permits the driver to effect a continued depression of the pedal 52 after the clutch surfaces 37, 38 have been brought into engagement. According to a modification the clutch 9 may be dispensed with, in which case, when the speed of rotation of the elements 22, 22a exceeds the limiting value corresponding to the resistance of the spring 28, the elements move outwardly into contact with the casing 1, which would then oppose the excess centrifugal force.